People have been harnessing wind energy for over seven thousand years to propel boats, pump water, process foodstuffs and produce electricity, among other things. Research and development related to the harnessing of wind energy has increased the amount of energy that may be harnessed from the wind in a specific area and/or has reduced the costs associated with harnessing the energy when compared to the amount of wind energy harnessed. Generally, the most common modern method of harnessing wind energy is the production of electrical energy utilizing a wind turbine.
Modern wind turbines are designed to produce a maximum amount of electrical energy at the lowest possible cost in a particular geographical area. The costs associated with a wind turbine can generally be divided into acquisition costs and life cycle costs, of which, acquisition costs are generally significantly higher. Portions of the cost and performance of a wind turbine are apportioned into some type of control system that controls the operation of the wind turbine at high wind speeds to prevent structural damage to the wind turbine structure and at lower wind speeds to maximize the energy extracted from the wind. Modern wind turbines are generally controlled in high and low winds by either a pitch control system or a passive stall control system.
Referring to FIGS. 1 and 7, prior art wind turbines 10′ utilizing the stall control system include turbine blades 14′ that have a specific chord to thickness ratio and a shape that is optimized to extract a maximum amount of energy from a specific optimum wind speed range 60′ that passes by the blades 14′ and through a swept area A′ of the blades 14′. The shape of the blades 14′ may be based, at least partially, on the wind conditions at the geographic location of the wind turbine 10′. The prior art turbine blades 14′ that utilize the stall control system have been optimized to extract a near theoretical maximum amount of energy from wind that passes through the swept area A′ within the optimum wind speed range 60′. During high speed wind conditions or highly variable wind conditions, the blades 14′ are designed to stall to avoid structural damage to the blades 14′ and/or drive train of the wind turbine 10′.
The stall control wind turbine 10′ is designed to stall to avoid excessive structural loading on the drive train and blades 14′ and to be shutdown in wind speeds that exceed a shutdown wind speed 50′ (see also FIG. 8). The stall and shutdown conditions of the wind turbine 10′ are undesirable because the wind turbine 10′ either is not efficiently generating power in variable wind conditions or stops generating power, thereby resulting in lost revenue and/or interruption in power production.
The stall control system is generally utilized because of its simplicity and low acquisition costs. However, stall control wind turbines 10′ generally do not operate efficiently, or at all, in highly variable wind speeds and/or wind speeds outside of the optimum wind speed range 60′. Further, the stall controlled wind turbine 10′ is subjected to high structural loads during highly variable wind speeds, which may damage the wind turbine 10′ and/or cause fatigue problems in structural components of the wind turbine 10′.
Alternative to the stall control wind turbines 10′, a pitch controlled wind turbine 10′ may be utilized to extract energy from the wind. The pitch controlled wind turbines 10′ are generally well known in the art and employ a pitch control system that adjusts a pitch angle of the blades 14′ to optimize the energy production of the wind turbine 10′. The pitch control system permits adjustments to the pitch of the blades 14′ to optimize the lift of the blades 14′ by setting the pitch of the blade 14′ at an optimum position relative to a wind blowing in a specific direction at various speeds through the swept area A′. Altering the pitch of the blades 14′ to control the lift characteristics permits the pitch controlled wind turbine 10′ to operate more efficiently in variable wind speeds and to generally operate in a slightly greater optimum wind speed range 60′ than the stall controlled wind turbines 10′. However, pitch control wind turbines 10′ generally have a slow rate of response to highly variable wind speeds and directions. In addition, the pitch control wind turbines 10′, similar to the stall controlled wind turbines 10′, are limited by the above-described structural load considerations. The structural load considerations may limit the length L′ of the blades 14′ and the optimum wind speed range 60′ that the pitch control wind turbine 10′ may operate in. Accordingly, the pitch controlled wind turbines 10′ are frequently not producing power because wind speeds in a specific area are outside of the optimum wind speed range 60′, which causes power interruptions, wind turbine 10′ downtime and loss of revenue. In addition, the pitch controlled wind turbines 10′ are often subjected to high structural loads in highly variable or blustery wind conditions due to the relatively slow rate of response of the pitch control system to highly variable wind speeds and directions.
The prior art wind turbine blades 14′ utilizing stall and pitch control are designed such that they begin producing power at a cut in wind speed 48′, continue to produce power as the wind speed increases, begin producing a maximum power Pmax′ at a lower rated speed 58′ and lose lift and stall or shutdown at and above the shutdown speed 50′. In wind speeds above the shutdown speed 50′, the wind turbine 10′ is shutdown to minimize the above-discussed structural loads and possible damage resulting therefrom. As can be seen graphically in FIGS. 1, 7 and 8, the prior art stall and pitch controlled wind turbines 10′ with the conventional blades 14′ are limited in both their range of operation and power production.
Generally, the stall and pitch control wind turbines 10′ may be efficiently operated in a geographical area that has low wind variability with a mean annual wind speed of more than six meters per second (6 m/s) and wind speeds that do not frequently exceed approximately twenty-five meters per second (25 m/s). In wind conditions exceeding approximately twenty-five meters per second (25 m/s), the wind turbine 10′ must be shutdown to avoid structural damage. Unfortunately, geographical areas that have mean annual wind speeds greater than approximately six meters per second (6 m/s) but less than twenty-five meters per second (25 m/s), low peak wind speeds and low wind speed variability are highly limited. In addition, such ideal geographical locations are generally located great distances from populated areas. Therefore, wind turbines that operate in an expanded wind speed range, operate effectively in variable wind conditions and are able to efficiently and safely extract power from high speed winds are desirable.
The primary technical barrier to extracting the maximum amount of power from the wind at a given location is the rate and/or magnitude of response of the control system and its impact on the efficiency and the above-described structural considerations of the wind turbine 10′. These barriers may drive the acquisition costs of the wind turbine 10′ and the length of the blades 14′ that may be utilized. The advanced aerodynamic control system for a high output wind turbine is a device utilized to, increase the energy capture of the wind turbine, maintain or reduce the operating and shutdown structural loads on the wind turbine, increase the operating range of the wind turbine and/or overcome the length limitations of the prior art wind turbine blades 14′. A preferred embodiment of the control system of the present invention is able to reduce the acquisition costs of the wind turbine components and decrease the amount of time that the wind turbine spends in shutdown mode by increasing the energy capture of the blades while maintaining and, in some ranges, reducing the structural loads on the wind turbine. The ability to increase the length of the blades results in an increase in the swept area of the wind turbine blades and a quadratic increase in energy that may be extracted from a specific wind speed. The preferred control system of the present invention also permits operation of the wind turbine in an expanded wind speed range. The control system of the present invention overcomes some of the above-described limitations of the prior art wind turbine and blades through the use of the control system with a Coanda-type turbine blade. The Coanda-type blade permits relatively quick modification of the lift and drag properties of the wind turbine blades in various wind conditions. Specifically, the use of the control system permits operation of the wind turbine in a wider optimum wind speed range with similar or reduced structural loads on the wind turbine and, therefore, reduced component costs and extended component life. The control system of the wind turbine also enhances the efficient power extraction from the wind over a useful range of wind speeds.
Alternatively, in another embodiment of the present invention, the control system may be utilized with Coanda-type blades having a similar or equivalent length when compared to the prior art wind turbine blades. In such a configuration, the control system and Coanda-type blade of the present invention permit operation of the wind turbine in wind speed ranges outside of the operating range of a conventional state of the art wind turbine, decreases the structural loads encountered by the wind turbine when compared to the conventional wind turbine and may significantly reduce the life cycle and acquisition costs of the wind turbine when compared to the conventional wind turbine designed for similar conditions. Acquisition costs may be reduced, in part, due to the reduction in structural loads on the wind turbine. The reduction in structural loads encountered by the wind turbine using the control system and blades of the present invention may permit a wind turbine to operate in regions with extreme wind conditions. The wind turbine of this alternative embodiment may also operate more efficiently throughout the operating wind speed range when compared to the conventional wind turbine, thereby producing more power and revenue over the life of the wind turbine.